Out of memory error while converting pdfs to excel 0x8007000E (E_OUTOFMEMORY)

I am developing a program that converts pdf documents to excel files. There are about 1000 pdf files to convert. But I got this error while processing the 234th file. Here's the important code.

private void getFullFileContent()
    {
        Excel.Application objExcel = new Excel.Application();
        objExcel.Visible = true;
        Excel.Workbook objBook = objExcel.Workbooks.Add(System.Reflection.Missing.Value);
        Excel.Worksheet objSheet;

        Excel.Range objRange=null;

        DateTime endDate, startDate=System.DateTime.Now;



        string[] pdfFiles = Directory.GetFiles(folderBrowserDialog1.SelectedPath, "*.pdf");
        for (int i = 1; i <= pdfFiles.Length; i++)
        {
            objSheet = (Excel.Worksheet)objBook.Worksheets.get_Item(1);
            string bColumn = "B" + i,aColumn="A"+i;

            objRange = objSheet.get_Range(aColumn, System.Reflection.Missing.Value);
            objRange.set_Value(System.Reflection.Missing.Value, pdfFiles[i-1].Substring(pdfFiles[i-1].LastIndexOf('\\') + 1));
            objRange = objSheet.get_Range(bColumn, System.Reflection.Missing.Value);
            objRange.set_Value(System.Reflection.Missing.Value, ConvertPdfToText(pdfFiles[i - 1]));
            label4.Text = pdfFiles[i].Substring(pdfFiles[i].LastIndexOf('\\')+1);
            label6.Text = "Remaining File: "+(pdfFiles.Length - i).ToString();
            endDate = System.DateTime.Now;
            label5.Text = "Total time: " + (endDate - startDate).Hours.ToString() + ":" + (endDate - startDate).Minutes.ToString() + ":" + (endDate - startDate).Seconds.ToString();
            GC.Collect();
        }

        try
        {

              objBook.SaveAs("Training Data.xlsx");
              MessageBox.Show("Your PDF files converted and printed into \"Training Data.xlsx\"");
        }
        catch (Exception)
        {                
            throw;
        }



    }


   private string ConvertPdfToText(string path)
    {
        StringBuilder text = new StringBuilder();
        string fileName = path;
        string strFileContent = "";
        if (File.Exists(fileName))
        {
            PdfReader pdfReader = new PdfReader(fileName);

            for (int page = 1; page <= pdfReader.NumberOfPages; page++)
            {
                ITextExtractionStrategy strategy = new SimpleTextExtractionStrategy();
                string currentText = PdfTextExtractor.GetTextFromPage(pdfReader, page, strategy);

                currentText = Encoding.UTF8.GetString(ASCIIEncoding.Convert(Encoding.Default, Encoding.UTF8, Encoding.Default.GetBytes(currentText)));
                text.Append(currentText);

                strFileContent += currentText;
            }
            pdfReader.Close();
        }
        return strFileContent;
    }

How large are your files? Maybe you could try using a memory profiler like RedGate Ants or JetBrains dotTrace to figure out where memory is leaking (while using a smaller batch).

Also this piece of code could be outside the for loop from getFullFileContent():

objSheet = (Excel.Worksheet)objBook.Worksheets.get_Item(1)